Liquid crystal display device and method of fabricating the same

ABSTRACT

A liquid crystal display device including a first substrate, a second substrate facing and spaced away from the first substrate, a liquid crystal layer sandwiched between the first and second substrates, a switching device formed on the first substrate, a first electrically insulating film randomly patterned on the first substrate, a second electrically insulating film covering the first electrically insulating film therewith, and having a wavy surface, and a reflection electrode formed on the second electrically insulating film, and electrically connected to an electrode of the switching device, wherein a light passing through the second substrate and the liquid crystal layer is reflected at the reflection electrode, and the second electrically insulating film extends outwardly from the first electrically insulating film by a certain length at an end of a display region in which images are to be displayed, such that a step formed by the first and second electrically insulating films in the vicinity of the end of the display region is smoothed.

This application is a division of co-pending application Ser. No.11/178,463 filed Jul. 12, 2005, which is a division of application Ser.No. 10/059,183 filed on Jan. 31, 2002, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a liquid crystal display device and a method offabricating the same.

2. Description of the Related Art

A reflection type liquid crystal display device reflects an incidentlight at a reflection electrode formed therein towards a viewer.Accordingly, a reflection type liquid crystal display device is notnecessary to include a light source such as a back light device, andthus, consumes less power and can be fabricated thinner and lighter thana light-transmission type liquid crystal display device. A reflectiontype liquid crystal display device is used mainly in a handycommunication terminal.

Hereinbelow is explained a conventional reflection type liquid crystaldisplay device with reference to FIG. 1 which is a plan view of aconventional reflection type liquid crystal display device, FIG. 2 whichis a cross-sectional view taken along the line II-II in FIG. 1, andFIGS. 3A to 3H which are cross-sectional views each illustrating a stepof a method of fabricating a substrate on which a thin film transistor(TFT) is to be fabricated. FIG. 1 illustrates pixels located at an outerperiphery of a display area in which images are to be displayed.Electrode terminals and other parts are formed in areas located at upperand left sides of the illustrated pixels, outside the display area.

First, a structure of a conventional reflection type liquid crystaldisplay device is explained hereinbelow with reference to FIGS. 1 and 2.

The illustrated conventional reflection type liquid crystal displaydevice is comprised of a TFT substrate 5 on which a thin film transistor(TFT) is formed, an opposing substrate 6 facing and spaced away from theTFT substrate 5, and a liquid crystal display layer 4 sandwiched betweenthe TFT substrate 5 and the opposing substrate 6.

The TFT substrate 5 is comprised of gate lines 1, drain lines 2extending perpendicularly to the gate lines 1, switching devices eachcomprised of a thin film transistor 3 formed in each of pixel areasdefined by the gate lines 1 and the drain lines 2, a reflectionelectrode 18 which reflects a light entering the pixel areas and appliesa voltage to liquid crystal molecules in the liquid crystal layer 4, afirst electrically insulating film 16 formed on the TFT substrate 5, anda second electrically insulating film 17 which cooperates with the firstelectrically insulating film 16 to present a wavy surface to thereflection electrode 18.

The thin film transistor 3 has a gate electrode 11 electricallyconnected to the gate line 1, a drain electrode 14 electricallyconnected to the drain line 2, and a source electrode 15 electricallyconnected to the reflection electrode 18.

As illustrated in FIG. 2, the TFT substrate 5 is comprised further of afirst substrate 10 on which the gate electrode 11 is formed, a gateinsulating film 12 formed entirely on the first substrate 10, anamorphous silicon layer 13 a formed on the gate insulating film 12, andn+ amorphous silicon layers 13 b formed on the amorphous silicon layer13 a.

The drain electrode 14 and the source electrode 15 extend covering boththe n+ amorphous silicon layers 13 b and the gate insulating film 12therewith.

The first electrically insulating film 16 is randomly formed in each ofpixels in the display area, and is covered with the second electricallyinsulating film 17 to smooth steps formed by the first electricallyinsulating film 16. The reflection electrode 18 has a wave surfaceshowing a certain optical reflection characteristic, reflecting a wavysurface of the second electrically insulating film 17.

As illustrated in FIG. 2, the reflection electrode 18 is electricallyconnected to the source electrode 15 at a contact hole 19.

The opposing substrate 6 is comprised of a second substrate 20, a colorfilter 21 formed on a first surface of the second substrate 20, a commonelectrode 22 through which a voltage is applied to liquid crystalmolecules in the liquid crystal layer 4, and a polarizing plate 23formed on a second surface of the second substrate 20.

Liquid crystal molecules in the liquid crystal layer 4 are controlled bya voltage applied across the TFT substrate 5 and the opposing substrate6.

An incident light 24 passing through the opposing substrate 6 and theliquid crystal layer 4 is reflected at the reflection electrode 18having the wavy surface, and then, passes again through the liquidcrystal layer 4 and the opposing substrate 6, and leaves the liquidcrystal display device as an out-going light 25.

In the conventional liquid crystal display device, steep steps formed bythe first electrically insulating film 16 randomly formed on the TFTsubstrate 5 are smoothed by the second electrically insulating film 17thinner than the first electrically insulating film 16, as mentionedearlier. As a result, the reflection electrode 18 has a sufficientlywavy surface at which the incident light 24 is randomly reflected,ensuring that images can be displayed on a screen with uniformbrightness.

Hereinbelow is explained a method of fabricating the TFT substrate 5 inthe above-mentioned conventional liquid crystal display device withreference to FIGS. 3A to 3H. The thin film transistor 3 acting as aswitching device has a reverse-stagger structure.

First, as illustrated in FIG. 3A, the gate electrode 11 and the gateline 1 are formed on the first substrate 10. Then, the gate insulatingfilm 12 is formed on the first substrate 10, covering the gate electrode11 therewith. Then, the amorphous silicon layer 13 a is formed on thegate insulating film 12 above the gate electrode 11, and subsequently,the n+ amorphous silicon layer 13 b is formed on the amorphous siliconlayer 13 a.

Then, the drain electrode 14 and the source electrode 15 are formedpartially covering the n+ amorphous silicon layer 13 b therewith andfurther partially covering the gate insulating film 12 therewith.

Then, the n+ amorphous silicon layers 13 b is etched in its exposed areawith the drain and source electrodes 14 and 15 being used as a mask, tothereby fabricate the thin film transistor 3. Then, the thin filmtransistor 3 is covered with a passivation film (not illustrated).

Then, as illustrated in FIG. 3B, the first electrically insulating films16 composed of a resin are randomly formed in each of pixel regions. Theelectrically insulating films 16 are formed to have a thickness equal toor greater than a predetermined thickness in order to provideappropriate optical reflection characteristic to the reflectionelectrode 18.

Then, as illustrated in FIG. 3C, the first electrically insulating films16 are heated to turn their sharp corners into rounded corners.

Then, as illustrated in FIG. 3D, the first electrically insulating films16 are covered with the second electrically insulating film 17. Sincethe second electrically insulating film 17 is formed in order to smoothsteps formed by the first electrically insulating films 16, if it is toothin, the steps formed by the first electrically insulating films 16remain as they are, and if it is too thick, the second electricallyinsulating film 17 would have a planar surface. Hence, a thickness ofthe second electrically insulating film 17 is determined taking theoptical reflection characteristic of the reflection electrode 18 intoconsideration.

Then, the second electrically insulating film 17 is removed in an areaoutside the display area, and concurrently removed partially above thesource electrode 15 to form the contact hole 19 through which thereflection electrode 18 is electrically connected to the sourceelectrode 15.

Then, as illustrated in FIG. 3E, a metal 18 b having high reflectivityis deposited all over the first substrate 10.

Then, as illustrated in FIG. 3F, the metal 18 b is entirely covered witha resist 26.

Then, as illustrated in FIG. 3G, the resist 26 is exposed to a light andsubsequently developed such that a resist pattern 26 a covers only anarea in which the reflection electrode 18 is to be formed. Then, themetal 18 b is etched for removal with the resist pattern 26 being usedas a mask.

Thus, as illustrated in FIG. 3H, the reflection electrode 18 composed ofthe metal 18 b is formed covering the second electrically insulatingfilm 17 therewith. Then, the resist pattern 26 a is removed.

The resultant reflection electrode 18 is electrically connected to thesource electrode 15 in each of pixels. The reflection electrode 18 isremoved at a boundary between pixel areas, that is, on both the gateline 1 and the drain line 2, and further in an area (an area located atthe left in FIG. 3H) where electrode terminals are to be formed whicharea is outside the display area, in order that the reflection electrode18 acts as a pixel electrode to apply a voltage to liquid crystalmolecules in the liquid crystal layer 4.

However, the above-mentioned conventional liquid crystal display deviceand the above-mentioned method of fabricating the same are accompaniedwith the following problems.

In the step having been explained with reference to FIG. 3D, the secondelectrically insulating film 17 formed for smoothing the steps formed bythe first electrically insulating films 16 is formed also on both thegate line 1 and the drain line 2 between adjacent pixels, in order tomake it easy to remove the reflection electrode 18. In the area (whichis located at the left in FIG. 3H) where electrode terminals are to beformed, located outside the display area, the second electricallyinsulating film 17 is removed at the same location as the firstelectrically insulating film 16, in order to render the area as small aspossible and thereby fabricate a liquid crystal display device in asmall size. As a result, as illustrated in FIG. 3H, the first and secondelectrically insulating films 16 and 17 have a steep cross-section at anend thereof.

Herein, it is assumed that the resist 26 is deposited entirely over thefirst substrate 10 with the first and second electrically insulatingfilm 16 and 17 having a steep cross-section. The resist 26 would have adesigned thickness in an area where the second electrically insulatingfilm 17 covers the first electrically insulating film 16 therewith tothereby have a smooth upper surface, that is, in pixels or on the gateline 1 and the drain line 2 between adjacent pixels. In contrast, in thearea where electrode terminals are to be formed, located outside thedisplay area, the resist 26 would gather due to the steep cross-section,and resultingly, would have a thickness greater than a designedthickness.

Since the conditions for carrying out exposure of the resist 26 to alight and development of the resist 26 are determined based on a resistexisting between pixels which resist is required to be exactlypatterned, the resist 26 could not be completely removed at an end ofthe first and second electrically insulating films 16 and 17 having agreat thickness, resulting in resist residue 26 b, as illustrated inFIG. 3G.

The resist residue 26 b would prevent the metal 18 b existing therebelowfrom being etched, resulting in an non-removed portion 18 a of the metal18 b, as illustrated in FIG. 3H.

If the portion 18 a of the metal 18 b remains not removed in an areawhere the metal 18 b has to be all removed, as mentioned above and asillustrated in FIG. 3H, there would be unintentionally generated aparasitic capacity between the non-removed portion 18 a and the gate anddrain lines 1 and 2, resulting in remarkable degradation in displayquality in the liquid crystal display device.

As an alternative, if the non-removed portion 18 a of the metal 18 bbridges over adjacent pixels, there would be caused a problem that theresultant reflection electrode 18 falls into short-circuit.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems in the conventional liquidcrystal display device and the method of fabricating the same, it is anobject of the present invention to provide a liquid crystal displaydevice and a method of fabricating the same both of which are capable ofpreventing unintentional generation of a parasitic capacity caused by anon-removed portion of a reflection electrode and further preventing areflection electrode from falling into short-circuit between adjacentpixels.

In one aspect of the present invention, there is provided a liquidcrystal display device including (a) a first substrate, (b) a secondsubstrate facing and spaced away from the first substrate, (c) a liquidcrystal layer sandwiched between the first and second substrates, (d) aswitching device formed on the first substrate, (e) a first electricallyinsulating film randomly patterned on the first substrate, (f) a secondelectrically insulating film covering the first electrically insulatingfilm therewith, and having a wavy surface, and (g) a reflectionelectrode formed on the second electrically insulating film, andelectrically connected to an electrode of the switching device, whereina light passing through the second substrate and the liquid crystallayer is reflected at the reflection electrode, the second electricallyinsulating film extends outwardly from the first electrically insulatingfilm by a certain length at an end of a display region in which imagesare to be displayed, such that a step formed by the first and secondelectrically insulating films in the vicinity of the end of the displayregion is smoothed.

It is preferable that the certain length is in the range of about 10 μmto about 12 μm both inclusive.

It is preferable that the second electrically insulating film has athickness in the range of about 0.3 μm to about 1.5 μm both inclusive.

It is preferable that the first electrically insulating film has athickness in the range of about 1 μm to about 3 μm both inclusive.

For instance, the second electrically insulating film may be composed ofthermo-flexible organic or inorganic material.

For instance, the first and second electrically insulating films may becomposed of different materials from each other.

For instance, the first and second electrically insulating films may becomposed of the same material having different viscosities from eachother.

For instance, the first and second electrically insulating films may becomposed of a combination of organic and inorganic materials.

There is further provided a liquid crystal display device including (a)a first substrate, (b) a second substrate facing and spaced away fromthe first substrate, (c) a liquid crystal layer sandwiched between thefirst and second substrates, (d) a switching device formed on the firstsubstrate, (e) a first electrically insulating film randomly patternedon the first substrate, (f) a second electrically insulating filmcovering the first electrically insulating film therewith, and having awavy surface, and (g) a reflection electrode formed on the secondelectrically insulating film, and electrically connected to an electrodeof the switching device, wherein a light passing through the secondsubstrate and the liquid crystal layer is reflected at the reflectionelectrode, the second electrically insulating film extends inwardly fromthe first electrically insulating film by a certain length at a contactregion where the reflection electrode is electrically connected to theelectrode of the switching device, such that a step formed by the firstand second electrically insulating films in the vicinity of the contactregion is smoothed.

There is still further provided a liquid crystal display deviceincluding (a) a first substrate, (b) a second substrate facing andspaced away from the first substrate, (c) a liquid crystal layersandwiched between the first and second substrates, (d) a switchingdevice formed on the first substrate, (e) an electrically insulatingfilm formed on the first substrate, and defined by a thick region and athin region, the electrically insulating film having a wavy surface, and(f) a reflection electrode formed on the electrically insulating film,and electrically connected to an electrode of the switching device,wherein a light passing through the second substrate and the liquidcrystal layer is reflected at the reflection electrode, the thin regionextends outwardly from the thick region by a certain length at an end ofa display region in which images are to be displayed, such that a stepformed by the electrically insulating film in the vicinity of the end ofthe display region is smoothed.

There is yet further provided a liquid crystal display device including(a) a first substrate, (b) a second substrate facing and spaced awayfrom the first substrate, (c) a liquid crystal layer sandwiched betweenthe first and second substrates, (d) a switching device formed on thefirst substrate, (e) an electrically insulating film formed on the firstsubstrate, and defined by a thick region and a thin region, theelectrically insulating film having a wavy surface, and (f) a reflectionelectrode formed on the electrically insulating film, and electricallyconnected to an electrode of the switching device, wherein a lightpassing through the second substrate and the liquid crystal layer isreflected at the reflection electrode, the thin region extends inwardlyfrom the thick region by a certain length at a contact region where thereflection electrode is electrically connected to the electrode of theswitching device, such that a step formed by the electrically insulatingfilm in the vicinity of the contact region is smoothed.

In another aspect of the present invention, there is provided a methodof fabricating a liquid crystal display device, including the steps atleast of (a) randomly patterning a first electrically insulating film ona first substrate on which a switching device is fabricated, (b)covering the first electrically insulating film with a secondelectrically insulating film, and (c) forming a reflection electrode ona wavy surface of the first and second electrically insulating filmssuch that the reflection electrode is electrically connected to anelectrode of the switching device, the reflection electrode reflecting alight passing through both a second substrate facing and spaced awayfrom the first substrate and a liquid crystal layer sandwiched betweenthe first and second substrates, the step (b) including (b1) forming thesecond electrically insulating film over the first substrate such thatthe first electrically insulating film is entirely covered with thesecond electrically insulating film, and (b2) partially removing thesecond electrically insulating film such that the second electricallyinsulating film extends outwardly from the first electrically insulatingfilm by a certain length at an end of a display region in which imagesare to be displayed, thereby a step formed by the first and secondelectrically insulating films in the vicinity of the end of the displayregion is smoothed.

It is preferable that the step (c) includes the steps of (c1) depositinga material of which the reflection electrode is composed, entirely overthe second electrically insulating film, (c2) coating a resist over thematerial, (c3) removing the resist in an area in which the material isto be removed, and (c4) etching the material with the resist being usedas a mask.

There is further provided a method of fabricating a liquid crystaldisplay device, including the steps at least of (a) randomly patterninga first electrically insulating film on a first substrate on which aswitching device is fabricated, (b) covering the first electricallyinsulating film with a second electrically insulating film, and (c)forming a reflection electrode on a wavy surface of the first and secondelectrically insulating films such that the reflection electrode iselectrically connected to an electrode of the switching device, thereflection electrode reflecting a light passing through both a secondsubstrate facing and spaced away from the first substrate and a liquidcrystal layer sandwiched between the first and second substrates, thestep (b) including (b1) forming the second electrically insulating filmover the first substrate such that the first electrically insulatingfilm is entirely covered with the second electrically insulating film,and (b2) partially removing the second electrically insulating film suchthat the second electrically insulating film extends inwardly from thefirst electrically insulating film by a certain length at a contactregion where the reflection electrode is electrically connected to theelectrode of the switching device, thereby a step formed by the firstand second electrically insulating films in the vicinity of the contactregion is smoothed.

It is preferable that the step (c) includes the steps of (c1) depositinga material of which the reflection electrode is composed, entirely overthe second electrically insulating film, (c2) coating a resist over thematerial, (c3) removing the resist in an area in which the material isto be removed, and (c4) etching the material with the resist being usedas a mask.

There is still further provided a method of fabricating a liquid crystaldisplay device, including the steps at least of (a) randomly patterningan electrically insulating film on a first substrate on which aswitching device is fabricated, the electrically insulating film havinga wavy surface, and (b) forming a reflection electrode on the wavysurface of the electrically insulating film such that the reflectionelectrode is electrically connected to an electrode of the switchingdevice, the reflection electrode reflecting a light passing through botha second substrate facing and spaced away from the first substrate and aliquid crystal layer sandwiched between the first and second substrates,the step (b) including (b1) forming the electrically insulating filmover the first substrate, and (b2) patterning the electricallyinsulating film into a removal region in which the electricallyinsulating film is completely removed, a thin region in which theelectrically insulating film remains as a thin film, and a thick regionin which the electrically insulating film remains as a thick film suchthat the thin region extends outwardly from the thick region by acertain length at an end of a display region in which images are to bedisplayed, thereby a step formed by the electrically insulating film inthe vicinity of the end of the display region is smoothed.

It is preferable that the electrically insulating film is patterned inthe step (b2) in single exposure to a light through the use of ahalf-tone mask having a light-permeable portion for defining the removalregion, a half-light-permeable portion for defining the thin region, anda light-impermeable portion for defining the thick region.

It is preferable that the half-light-permeable portion is locatedadjacent to the light-permeable portion.

It is preferable that the electrically insulating film is patterned inthe step (b2) in single exposure to a light through the use of a photomask having a light-permeable portion for defining the removal region,and a half-light-permeable portion for defining the thin region.

It is preferable that the electrically insulating film is patterned inthe step (b2) in single exposure to a light through the use of a photomask having such a fine pattern that a light to be directed to the thinregion is attenuated.

There is yet further provided a method of fabricating a liquid crystaldisplay device, including the steps at least of (a) randomly patterningan electrically insulating film on a first substrate on which aswitching device is fabricated, the electrically insulating film havinga wavy surface, and (b) forming a reflection electrode on the wavysurface of the electrically insulating film such that the reflectionelectrode is electrically connected to an electrode of the switchingdevice, the reflection electrode reflecting a light passing through botha second substrate facing and spaced away from the first substrate and aliquid crystal layer sandwiched between the first and second substrates,the step (b) including (b1) forming the electrically insulating filmover the first substrate, and (b2) patterning the electricallyinsulating film into a removal region in which the electricallyinsulating film is completely removed, a thin region in which theelectrically insulating film remains as a thin film, and a thick regionin which the electrically insulating film remains as a thick film suchthat the thin region extends inwardly from the thick region by a certainlength at a contact region where the reflection electrode iselectrically connected to the electrode of the switching device, therebya step formed by the electrically insulating film in the vicinity of thecontact region is smoothed.

The advantages obtained by the aforementioned present invention will bedescribed hereinbelow.

In accordance with the present invention, the second electricallyinsulating film is designed to extend outwardly from the firstelectrically insulating film by a certain length at an end of a displayregion, and is further designed to have a thickness in a predeterminedrange. As an alternative, the second electrically insulating film isdesigned to extend inwardly from the first electrically insulating filmby a certain length at a contact region. As a result, it would bepossible to smooth a step formed by the first and second electricallyinsulating films in the vicinity of an end of the display region. Thisensures that it would be possible to prevent a resist used forpatterning the reflection electrode from gathering as a resist residueat an end of the first and second electrically insulating films. Thus,generation of an non-removed portion of a reflection electrode caused bythe resist residue would be prevented, ensuring that it would bepossible to avoid an unintentional parasitic capacity and preventadjacent pixels from short-circuiting with each other. As a result, thepresent invention provides a liquid crystal display device having nonon-uniformity in display and presenting high quality images.

Furthermore, the use of a half-tone mask or photo mask in the method offabricating a liquid crystal display device would make it possible toform the first and second electrically insulating films of a commonmaterial in a single step, ensuring reduction in the number offabrication steps.

The above and other objects and advantageous features of the presentinvention will be made apparent from the following description made withreference to the accompanying drawings, in which like referencecharacters designate the same or similar parts throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a conventional reflection type liquid crystaldisplay device.

FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1.

FIGS. 3A to 3H are cross-sectional views each illustrating a step of amethod of fabricating a substrate on which a thin film transistor (TFT)is to be fabricated, in the conventional reflection type liquid crystaldisplay device illustrated in FIG. 1.

FIG. 4 is a plan view of the reflection type liquid crystal displaydevice in accordance with the first embodiment of the present invention.

FIG. 5 is a cross-sectional view taken along the line V-V in FIG. 4.

FIGS. 6A to 6H are cross-sectional views each illustrating a step of amethod of fabricating a substrate on which a thin film transistor (TFT)is to be fabricated, in the reflection type liquid crystal displaydevice illustrated in FIG. 4.

FIG. 7 is a graph showing a relation between a thickness of a resist andlight exposure in the reflection type liquid crystal display device inaccordance with the first embodiment.

FIG. 8 is a graph showing a relation between a thickness of anelectrically insulating film at a periphery of the display area and athickness of a resist in the reflection type liquid crystal displaydevice in accordance with the first embodiment.

FIG. 9 is a graph showing a relation among a viscosity of a resin, anumber of revolution in spin-coating a resin and a thickness in thereflection type liquid crystal display device in accordance with thefirst embodiment.

FIGS. 10A to 10H are cross-sectional views each illustrating a step of amethod of fabricating a substrate on which a thin film transistor (TFT)is to be fabricated, in the reflection type liquid crystal displaydevice in accordance with the second embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments in accordance with the present invention will beexplained hereinbelow with reference to drawings.

First Embodiment

FIG. 4 is a plan view of a reflection type liquid crystal display devicein accordance with the first embodiment, and FIG. 5 is a cross-sectionalview taken along the line V-V in FIG. 4.

With reference to FIGS. 4 and 5, the reflection type liquid crystaldisplay device is comprised of a TFT substrate 5 on which a thin filmtransistor (TFT) is formed, an opposing substrate 6 facing and spacedaway from the TFT substrate 5, and a liquid crystal display layer 4sandwiched between the TFT substrate 5 and the opposing substrate 6.

The TFT substrate 5 is comprised of gate lines 1, drain lines 2extending perpendicularly to the gate lines 1, switching devices eachcomprised of a thin film transistor 3 formed in each of pixel areasdefined by the gate lines 1 and the drain lines 2, a reflectionelectrode 18 which reflects a light entering the pixel areas and appliesa voltage to liquid crystal molecules in the liquid crystal layer 4, afirst electrically insulating film 16 formed on the TFT substrate 5, anda second electrically insulating film 17 which cooperates with the firstelectrically insulating film 16 to present a wavy surface to thereflection electrode 18.

The thin film transistor 3 has a gate electrode 11 electricallyconnected to the gate line 1, a drain electrode 14 electricallyconnected to the drain line 2, and a source electrode 15 electricallyconnected to the reflection electrode 18.

As illustrated in FIG. 5, the TFT substrate 5 is comprised further of afirst substrate 10 on which the gate electrode 11 is formed, a gateinsulating film 12 formed entirely on the first substrate 10, anamorphous silicon layer 13 a formed on the gate insulating film 12, andn+ amorphous silicon layers 13 b formed on the amorphous silicon layer13 a.

The drain electrode 14 and the source electrode 15 extend covering boththe n+ amorphous silicon layers 13 b and the gate insulating film 12therewith.

The first electrically insulating film 16 is randomly formed in each ofpixels in the display area, and is covered with the second electricallyinsulating film 17 to smooth steps formed by the first electricallyinsulating film 16.

The first electrically insulating film 16 is randomly formed in thedisplay area in order to have uniform optical reflection characteristicall over the display area, whereas the first electrically film 16 is notformed in a terminal area located outside the display area, becauseelectrode terminals and other parts have to be formed in the terminalarea. In FIG. 4, the terminal area extends at the upper and left sidesof the illustrated pixels.

The second electrically insulating film 17 is continuously formed in thedisplay area without a contact hole 19, and slightly extends to theterminal area such that an end of the first electrically insulating film16 does not overlap an end of the second electrically insulating film17. This ensures that the display area has a smooth step at an endthereof.

As illustrated in FIG. 5, the reflection electrode 18 is electricallyconnected to the source electrode 15 at the contact hole 19 formedthrough the second electrically insulating film 17 above the sourceelectrode 15.

The reflection electrode 18 is necessary to be separated into pieces foreach of pixels, because the reflection electrode 18 acts also as a pixelelectrode for applying a voltage to liquid crystal molecules in theliquid crystal layer 4. Hence, as illustrated in FIG. 4, the reflectionelectrode 18 is separated along the gate lines 1 and the drain lines 2for each of pixels.

The opposing substrate 6 is comprised of a second substrate 20, a colorfilter 21 formed on a first surface of the second substrate 20, a commonelectrode 22 through which a voltage is applied to liquid crystalmolecules in the liquid crystal layer 4, and a polarizing plate 23formed on a second surface of the second substrate 20.

Liquid crystal molecules in the liquid crystal layer 4 are controlled bya voltage applied across the TFT substrate 5 and the opposing substrate6.

An incident light 24 passing through the opposing substrate 6 and theliquid crystal layer 4 is reflected at the reflection electrode 18having the wavy surface, and then, passes again through the liquidcrystal layer 4 and the opposing substrate 6, and leaves the liquidcrystal display device as an out-going light 25.

The reflection electrode 18 has a wave surface reflecting a wavy surfaceof the second electrically insulating film 17, and has an opticalreflection characteristic defined by angles of raised and recessedportions of the wave surface of the reflection electrode 18. Hence, theangles of the raised and recessed portions of the wave surface of thereflection electrode 18 are determined so as to provide a desiredoptical reflection characteristic to the reflection electrode 18. Forinstance, the raised and recessed portions may be defined by two or moreof a pitch between raised portion, a pitch between recessed portions, aheight of a raised portion, and a depth of a recessed portion.

A lower limit of a thickness of the first electrically insulating film16 is defined by the above-mentioned optical reflection characteristic,and further by a parasitic capacity. If the first electricallyinsulating film 16 is formed too thin, it would not be possible tosignificantly change a direction of reflection of the incident light 24,and a space between the reflection electrode 18 and the gate and drainlines 1 and 2 would be narrowed, resulting in an increase in a parasiticcapacity between the reflection electrode 18 and the gate and drainlines 1 and 2, and signal delay. As a result, a signal cannot beproperly transmitted, and an electric field between a signal line and apixel would be intensified, causing disturbance in alignment of liquidcrystal molecules, delay in a response, and degradation in quality ofdisplayed images.

From the above-mentioned standpoints, the first electrically insulatingfilm 16 is preferably designed to have a thickness in the range of about1 μm to about 3 μm.

Since the second electrically insulating film 17 is formed formoderately relaxing the raised and recessed portions of the firstelectrically insulating film 16 to smooth the wavy surface of the firstelectrically insulating film 16, if the second electrically insulatingfilm 17 is too thin, the second electrically insulating film 17 couldnot smooth the wavy surface of the first electrically insulating film16, whereas if the second electrically insulating film 17 is too thick,the second electrically insulating film 17 would cancel projections andrecesses of the first electrically insulating film 16, and would beflattened.

In the first embodiment, the second electrically insulating film 17 isdesigned to have such a thickness that resist residue does not remainnon-removed in an area outside the display area. In accordance with theresults of the experiments having been conducted by the inventors, ithas been found out that it is preferable for the second electricallyinsulating film 17 to have a thickness in the range of about 0.3 μm toabout 1.5 μm, and a distance between an end of the first electricallyinsulating film 16 to an end of the second electrically insulating film17 is preferably in the range of about 10 μm to about 12 μm.

Hereinbelow is explained the reason of selecting the above-mentionedfigures, with reference to FIGS. 7 to 9.

FIG. 7 shows a relation between a thickness of a resist and lightexposure necessary for removing the resist, FIG. 8 illustrates apositional relation between thicknesses of the first electricallyinsulating film 16, the second electrically insulating film 17 and theresist 26, and locations of ends of those, and FIG. 9 shows a relationamong a viscosity of a resin, a thickness of a resin and a number ofrevolution for spin-coating.

As illustrated in FIG. 7, greater light exposure is necessary forremoving a thicker resist. An accuracy with which a resist having acertain thickness is patterned is controllable for a certain range oflight exposure. In other words, the accuracy can be controlled in thecertain range of light exposure, though a pattern might be slightlythicker or thinner than designed. For instance, when a resist having athickness of 1 m is to be patterned, optimal light exposure is about 140mJ/cm². However, an accuracy with which the resist is patterned can becontrolled, if light exposure is in the range of about 80 mJ/cm² toabout 190 mJ/cm².

Conversely speaking, a thickness of a resist which can be patterned bycertain light exposure has a certain range. If a light is exposed to aresist by 190 mJ/cm², a resist having a thickness of 1 μm can beaccurately patterned, and further, a resist having a thickness of 2 μmcan be accurately patterned.

Applying the above-mentioned relation to the liquid crystal displaydevice, a thickness of the second electrically insulating film 17 and adistance between ends of the first and second electrically insulatingfilms 16 and 17 are determined in the first embodiment such that avariance in a thickness of a resist to be formed on the reflectionelectrode 18 is within such a range that an accuracy with which theresist is patterned is controllable.

As illustrated in FIG. 8, assuming that A indicates a thickness of thefirst electrically insulating film 16, B indicates a thickness of aplanarized portion of the second electrically insulating film 17, and Dindicates a thickness of a raised portion of the second electricallyinsulating film 17, a maximum variance in a thickness of the resist 26is defined by C or equal to B.

C=X+D+E−B−E

wherein X indicates a thickness of the first electrically insulatingfilm 16, and E indicates a thickness of the reflection electrode 18.

Herein, if the resist 26 had a thickness of 2 μm which is usuallyselected for photolithography, as is obvious in view of FIG. 7, lightexposure by which a resist having a thickness of 2 μm can be patternedis in the range of about 150 mJ/cm² to about 270 mJ/cm², and a resisthaving a thickness of 3.5 μm at maximum can be patterned by lightexposure of 270 mJ/cm².

Accordingly, the thickness C or B has to be equal to or smaller than 1.5μm (3.5 μm−2 μm=1.5 μm). If the first electrically insulating film 16 isdesigned to have a thickness in the range of 1 μm and 3 μm taking itsoptical reflection characteristic into consideration, an upper limit ofa thickness of the second electrically insulating film 17 is 1.5 μm, anda lower limit of a thickness of the same is preferably 0.3 μm for makinga step defined by the thickness C small.

The thickness B of a planarized portion of the second electricallyinsulating film 17 becomes smaller as a distance between the ends of thefirst and second electrically insulating films 16 and 17 becomesgreater, and approaches a certain thickness defined by a viscosity. Onthe other hand, if the distance is too long, the terminal area locatedoutside the display area would be too wide, resulting in that it wouldbe impossible to fabricate the liquid crystal display device in a smallsize. Hence, the distance is preferably equal to a distance by which thethickness B of a planarized portion of the second electricallyinsulating film 17 is fixed, that is, about 10 μm, and more preferablyequal to about 12 μm taking misregistration in a unit for exposing aresist to a light, into consideration.

In order to design the second electrically insulating film 17 to have athickness in the above-mentioned range, a viscosity of a resin and/or anumber of revolution at which a resin is spin-coated is(are) controlled.For instance, a thickness of the second electrically insulating film 17can be accurately controlled by spin-coating a resin in accordance withthe relation shown in FIG. 9.

In order to reduce a height of the second electrically insulating film17 (indicated as “B” in FIG. 8) in the terminal area located outside thedisplay area, an angle formed between a surface of the secondelectrically insulating film 17 and a surface of the first substrate 10might be determined to be in a certain range by improving wettability ofthe second electrically insulating film 17 with the first substrate 10or a passivation film such as a silicon nitride film. Specifically, evenif the second electrically insulating film 17 were thick, it would bepossible to avoid the problem of resist residue by applying surfacetreatment such as HMDS to the second electrically insulating film 17 tothereby improved the wettability, and make a contact angle small.

Thus, it would be possible to prevent resist residue from remainingnon-removed on the reflection electrode 18, by setting a thickness ofthe second electrically insulating film 17 or a distance between theends of the first and second electrically insulating films 16 and 17 tobe in a predetermined range. In addition, by relaxing a step formed bythe first and second electrically insulating films 16 and 17, aninclination angle formed by inner surfaces of the contact hole 19 couldbe controlled, ensuring that the reflection electrode 18 and the sourceelectrode 15 are kept in appropriate electrical contact with each other.

Hereinbelow is explained a method of fabricating the above-mentionedreflection type liquid crystal display device, with reference to FIGS.6A to 6H. In the method mentioned hereinbelow, the thin film transistor3 acting as a switching device has a reverse-stagger structure.

First, a metal layer composed of chromium, for instance, is formed onthe first substrate 10 composed of glass, for instance, by sputtering.Then, the metal layer is patterned into the gate line 1 and the gateelectrode 11 by photolithography and etching. The metal layer of whichthe gate line 1 and the gate electrode 11 are composed may be composedof a metal which has a low resistance and which can be readily patternedby photolithography, such as molybdenum, titanium, aluminum, or aluminumalloy as well as chromium. As an alternative, the metal layer may have amulti-layered structure having an aluminum layer and a barrier metallayer formed on the aluminum layer, wherein the barrier metal layer maybe composed of titanium.

Then, a silicon nitride film which will make the gate insulating film 12is formed all over the first substrate 10. Then, a non-doped amorphoussilicon film and a n+-doped amorphous silicon film are successivelyformed on the gate insulating film 12 by chemical vapor deposition(CVD). Thereafter, those amorphous silicon layers are patterned into theamorphous silicon layer 13 a and the n+ amorphous silicon layer 13 b.The amorphous silicon layer 13 a acts as an active layer in the thinfilm transistor 3, and the n+ amorphous silicon layer 13 b ensures ohmiccontact between the drain electrode 14, the source electrode 15 and theamorphous silicon layer 13 a.

Then, a chromium film is formed over the amorphous silicon layer 13 aand the n+ amorphous silicon layer 13 b by sputtering, and subsequently,patterned into the drain electrode 14 and the source electrode 15. Then,the n+ amorphous silicon layer 13 b is dry-etched in an area inalignment with a space formed between the drain electrode 14 and thesource electrode 15. This is for the purpose of preventing a currentfrom running directly through the drain electrode 14 and the sourceelectrode 15 via the n+ amorphous silicon layer 13 b.

Then, a silicon nitride film is formed over the first substrate 10 byCVD, and subsequently, patterned into a passivation film (notillustrated). The passivation film prevents impurities such as ions fromdiffusing into the amorphous silicon layer 13 a to thereby causemalfunction in the thin film transistor 3.

By carrying out the above-mentioned steps, the thin film transistor 3 isfabricated in the TFT substrate 5, as illustrated in FIG. 6A.

Then, as illustrated in FIG. 6B, the first electrically insulating film16 is formed on the gate insulating film 12 randomly in the displayarea.

Then, as illustrated in FIG. 6C, a process for changing a shape isapplied to the first electrically insulating film 16 to thereby roundthe first electrically insulating film 16 at corners.

Then, as illustrated in FIG. 6D, the second electrically insulating film17 is formed entirely covering the first electrically insulating film 16therewith, and then, there is formed the contact hole 19 throughout thesecond electrically insulating film 17 above the source electrode 15 forelectrically connecting the reflection electrode 18 and the sourceelectrode 15 to each other.

The first electrically insulating film 16 and the second electricallyinsulating film 17 are formed entirely in the display area, and thesecond electrically insulating film 17 is formed in such a way that thesecond electrically insulating film 17 extends outwardly beyond the endof the first electrically insulating film 16 in an area (that is, anarea located at the left in FIG. 6D) outside a pixel located at an outerperiphery of the display area, thereby avoiding a steep step to beformed by the first and second electrically insulating films 16 and 17.

The first electrically insulating film 16 may be composed ofphoto-insensitive resin or photosensitive resin.

If the first electrically insulating film 16 were composed ofphoto-insensitive resin, the method of fabricating the liquid crystaldisplay device would include the steps of (a) forming the firstelectrically insulating film 16 on the first substrate 19, (b) forming aresist for patterning the first electrically insulating film 16, (c)exposing the resist to a light, (d) developing the resist, (e) etchingthe first electrically insulating film 16, and (e) removing the resist.

If the first electrically insulating film 16 were composed ofphoto-sensitive organic or inorganic material, the method of fabricatingthe liquid crystal display device would include the steps of (a) formingthe first electrically insulating film 16 on the first substrate 19, (b)exposing the first electrically insulating film 16 to a light, and (c)developing the first electrically insulating film 16. The method mayomit the steps of forming a resist for patterning the first electricallyinsulating film 16, and removing the resist, in comparison with themethod in which the first electrically insulating film 16 is composed ofphoto-insensitive resin.

In the step having been explained with reference to FIG. 6C, thepatterned first electrically insulating film 16 is molten to haverounded corners, by annealing the first electrically insulating film 16at a temperature in the range of 80 to 300 degrees centigrade. As analternative, the first electrically insulating film 16 may be molten tohave rounded corners through the use of chemical instead of annealingthe first electrically insulating film 16. If the second electricallyinsulating film 17 only could present a sufficiently smooth wavysurface, it would not be always necessary to apply any process to thefirst electrically insulating film 16 to have rounded corners.

In the first embodiment, the first and second electrically insulatingfilms 16 and 17 were composed of polyimide commercially available fromNissan Kagaku Industry Co. Ltd., under the trade name of “RN-812”. Theconditions of coating the polyimide were as follows.

Number of revolution in spin-coating: 1200 r.p.m.

Temporarily baking temperature: 90 degrees centigrade

Temporarily baking time: 10 minutes

Baking temperature: 250 degrees centigrade

Baking time: 1 hour

The resist used for patterning the electrically insulating films 16 and17 were formed in the following conditions.

Number of revolution in spin-coating: 1000 r.p.m.

Temporarily baking temperature: 90 degrees centigrade

Temporarily baking time: 5 minutes

Post baking temperature (after patterning): 90 degrees centigrade

Post baking time: 30 minutes

The conditions for dry-etching the above-mentioned polyimide film withthe patterned resist being used as a mask were as follows.

Etching gas: FCl₄+O₂

Gas flow ratio (FCl₄/O₂): 0.5-1.5

Reaction pressure: 0.665-39.9 Pa

Plasma power: 100-300 W

The photolithography was carried out under ordinary resist processes.

Though the first and second electrically insulating films 16 and 17 arecomposed of the same organic resin in the first embodiment, they may becomposed of different materials from each other. The second electricallyinsulating film 17 could have a desired wavy surface by composing thefirst and second electrically insulating films 16 and 17 of acombination of inorganic material and organic material such as acrylicresin and polyimide resin, silicon nitride and acrylic resin, silicondioxide and polyimide or vice versa. In addition, if the secondelectrically insulating film 17 could be designed to have a sufficientlysmooth wavy surface, the first electrically insulating film 16 might beformed by evaporation, sputtering or CVD, as well as coating.

Then, as illustrated in FIG. 6E, a metal film 18 b composed of metalhaving a high reflectivity is formed entirely over the secondelectrically insulating film 17.

Then, as illustrated in FIG. 6F, a resist 26 is formed entirely coveringthe metal film 18 b.

Then, as illustrated in FIG. 6G, the resist 26 is patterned by beingexposed to a light and developed into a resist pattern 26 a coveringonly an area in which the reflection electrode 18 is to be formed.

Then, the metal film 18 b is etched with the resist pattern 26 a beingused as a mask. As a result, the metal film 18 b is removed in areasbetween adjacent pixels, specifically, above the gate line 1 and thedrain line 2, and further in the terminal area extending outside a pixellocated outermost in the display area, in order to allow the resultantreflection electrode 18 to be electrically connected to the sourceelectrode 15 in each of pixel and act as a pixel electrode.

Thereafter, the resist pattern 26 a is removed. Thus, there isfabricated the TFT substrate 5 as illustrated in FIG. 6H.

In the first embodiment, the reflection electrode 18 is composed ofaluminum which has high reflection ratio, and well matches with TFTprocess. By patterning the aluminum, the resultant reflection electrode18 acting as a pixel electrode and a reflection plate was formed. Thealuminum was wet-etched through the use of an etchant composed ofmixture of phosphoric acid, acetic acid and nitric acid and heated at 60degrees centigrade. However, it should be noted that the reflectionelectrode 18 might be composed any metal, if it had high reflectivity,other than aluminum. For instance, the reflection electrode 18 may becomposed of silver or silver alloy which has higher reflection ratiothan that of aluminum, ensuring brighter reflection performance thanthat of aluminum.

After alignment process was applied, the TFT substrate 5 and theopposing substrate 6 were adhered to each other by applying an epoxyadhesive to marginal portions of the substrates 5 and 6 with spacerssuch as plastic particles being sandwiched therebetween such that theelectrically insulating film 17 formed on the TFT substrate 5 and thecommon electrode 22 formed on the opposing substrate 6 faced each other.Thereafter, liquid crystal was injected into a space formed between theTFT substrate 5 and the opposing substrate 6 to thereby form the liquidcrystal layer 4.

In the above-mentioned liquid crystal display device in which the secondelectrically insulating film 17 cooperates with the first electricallyinsulating film 16 to form the wavy surface, and the reflectionelectrode 18 is formed on the wavy surface of the second electricallyinsulating film 17, the second electrically insulating film 17 isdesigned to have its end deviated from an end of the first electricallyinsulating film 16 in the terminal area extending outside a pixellocated outermost in the display area, specifically, the secondelectrically insulating film 17 extends outwardly from an end of thefirst electrically insulating film 16, and in addition, the secondelectrically insulating film 17 is designed to have a thickness in thepredetermined range. The above-mentioned structure of the liquid crystaldisplay device in accordance with the first embodiment would prevent avariance in a thickness of the resist used for patterning the reflectionelectrode 18, and thereby, further prevent unintentional parasiticcapacity and short-circuiting between adjacent pixels both caused by thenon-removed portion 18 a of the reflection electrode 18 (see FIG. 3G).

The thin film transistor 3 as a switching device may be comprised of astagger type thin film transistor or MIM diode. Even if the thin filmtransistor 3 is designed to have a reverse-stagger structure, thereverse-stagger structure is not to be limited to such a structure asmentioned in the first embodiment, but may have other structures.

Though each of the first and second substrates 10 and 20 is comprised ofa glass substrate in the first embodiment, they may be comprised of aplastic substrate, a ceramics substrate or a semiconductor substrate. Inaddition, the first embodiment may be applied to a display deviceincluding optical materials other than liquid crystal.

Second Embodiment

Hereinbelow is explained a method of fabricating a TFT substrate in thereflection type liquid crystal display device in accordance with thesecond embodiment, with reference to FIGS. 10A to 10H. The secondembodiment has an object of simplifying a method of fabricating a TFTsubstrate. Parts other than the TFT substrate in the second embodimentare fabricated in the same manner as the first embodiment.

Similarly to the first embodiment, first, a metal layer composed ofchromium, for instance, is formed on the first substrate 10 composed ofglass, for instance, by sputtering. Then, the metal layer is patternedinto the gate line 1 and the gate electrode 11 by photolithography andetching

Then, a silicon nitride film which will make the gate insulating film 12is formed all over the first substrate 10. Then, a non-doped amorphoussilicon film and a n+-doped amorphous silicon film are successivelyformed on the gate insulating film 12 by CVD. Thereafter, thoseamorphous silicon layers are patterned into the amorphous silicon layer13 a and the n+ amorphous silicon layer 13 b.

Then, a chromium film is formed over the amorphous silicon layer 13 aand the n+ amorphous silicon layer 13 b by sputtering, and subsequently,patterned into the drain electrode 14 and the source electrode 15. Then,the n+ amorphous silicon layer 13 b is dry-etched in an area inalignment with a space formed between the drain electrode 14 and thesource electrode 15, to thereby form a channel region.

Then, a silicon nitride film is formed over the first substrate 10 byCVD, and subsequently, patterned into a passivation film (notillustrated).

Thus, as illustrated in FIG. 10A, the thin film transistor 3 isfabricated on the first substrate 10.

Whereas the first and second electrically insulating films 16 and 17 areformed in separate steps in the above-mentioned first embodiment, theyare formed in a single step for simplifying the method of fabricatingthe liquid crystal display device, in the second embodiment, as follows.

As illustrated in FIG. 10B, an electrically insulating andphoto-sensitive film 16 a composed of organic or inorganic material iscoated all over the gate insulating film 12. Similarly to the firstembodiment, the electrically insulating and photo-sensitive film 16 a iscomprised of a polyimide film, and coated in the following conditions.

Number of revolution in spin-coating: 1200 r.p.m.

Temporarily baking temperature: 90 degrees centigrade

Temporarily baking time: 10 minutes

Baking temperature: 250 degrees centigrade

Baking time: 1 hour

The second embodiment is characterized in that a half-tone mask 27 isused for exposing the electrically insulating and photo-sensitive film16 a to a light, and developing the same. As illustrated in FIG. 10B,the half-tone mask 27 is designed to include a light-permeable portion27 a through which a light can pass, a half-light-permeable portion 27 bthrough which a light can pass after being attenuated to some degree,and a light-impermeable portion 27 c through which a light cannot pass.The half-tone mask 27 is positioned above the electrically insulatingfilm 16 a such that the light-impermeable portion 27 c will define araised portion, the half-light-impermeable portion 27 b will define arecessed portion, and the light-permeable portion 27 a will define anarea in which the electrically insulating film 16 a is entirely removed.

Then, the electrically insulating and photo-sensitive film 16 a isexposed to a light through the half-tone mask 27, and then, developed.As a result, as illustrated in FIG. 10C, the electrically insulating andphoto-sensitive film 16 a remains non-removed in an area in alignmentwith the light-impermeable portion 27 c, and is etched to some degree inan area in alignment with the half-light-permeable portion 27 b. Thus,the electrically insulating and photo-sensitive film 16 a has raised andrecessed portions, as illustrated in FIG. 10C.

In the half-tone mask 27, the half-light-permeable portion 27 b isdesigned to be located adjacent to the light-permeable portion 27 a inorder for the electrically insulating film 16 a not to have a steepstep.

By using the half-tone mask 27, the electrically insulating film 16 a isentirely removed in an area in alignment with the light-permeableportion 27 a by being exposed to a light for a long time or beingexposed to an intensive light, the electrically insulating film 16 a isremoved to some degree in an area in alignment with thehalf-light-permeable portion 27 b by being exposed to a light for ashort time or being exposed to a weak light, or the electricallyinsulating film 16 a is not removed at all in an area in alignment withthe light-impermeable portion 27 c by not being exposed to a light. As aresult, it would be possible to form both the first and secondelectrically insulating films 16 and 17 in a single step.

Then, as illustrated in FIG. 10D, a process for changing a shape isapplied to the electrically insulating film 16 a to thereby round theelectrically insulating film 16 a at corners thereof. Specifically, theelectrically insulating film 16 a is molten to have rounded corners, bybeing annealed at a temperature in the range of 80 to 300 degreescentigrade. As an alternative, the electrically insulating film 16 a maybe molten to have rounded corners through the use of chemical instead ofannealing the electrically insulating film 16 a. If the electricallyinsulating film 16 a could form the raised and recessed portions only bydevelopment, it would not be always necessary to apply anyshape-changing process to the electrically insulating film 16 a to haverounded corners.

Then, similarly to the first embodiment, a metal film 18 b composed ofmetal having a high reflectivity is formed entirely over the firstsubstrate 10, as illustrated in FIG. 10E.

Then, as illustrated in FIG. 10F, a resist 26 is formed entirelycovering the metal film 18 b.

Then, as illustrated in FIG. 10G, the resist 26 is patterned by beingexposed to a light and developed into a resist pattern 26 a coveringonly an area in which the reflection electrode 18 is to be formed.

Then, the metal film 18 b is etched with the resist pattern 26 a beingused as a mask. As a result, the metal film 18 b is removed in areasbetween adjacent pixels, specifically, above the gate line 1 and thedrain line 2, and further in the terminal area extending outside a pixellocated outermost in the display area, in order to allow the resultantreflection electrode 18 to be electrically connected to the sourceelectrode 15 in each of pixel and act as a pixel electrode.

Thereafter, the resist pattern 26 a is removed. Thus, there isfabricated the TFT substrate 5 as illustrated in FIG. 10H.

As mentioned above, the use of the half-tone mask 27 would make itpossible to form the electrically insulating film 16 a in a single step,ensuring reduction in the number of fabrication steps in comparison withthe first embodiment.

In addition, in the terminal area extending outside a pixel locatedoutermost in the display area, the electrically insulating film 16 a isremoved to some degree in area outside an area in which the electricallyinsulating film 16 a is not removed at all. Accordingly, theelectrically insulating film 16 a would not form a steep step, whichensures prevention of generation of the resist residue 26 b, and furtherof unintentional generation of parasitic capacity caused by thenon-removed portion 18 a of the reflection electrode 18.

In the above-mentioned second embodiment, the electrically insulatingfilm 16 a has raised and recessed portions through the use of thehalf-tone mask 27. Instead of using the half-tone mask 27, there may beused a first mask for removing the electrically insulating film 16 aonly to a degree and a second mask for not removing the electricallyinsulating film 16 a, wherein light exposure through the first andsecond masks are varied. As an alternative, the half-light-impermeableportion may be formed by means of a mask having a pattern smaller thanan upper limit of exposure ability. As an alternative, light exposuremay be varied in areas of the electrically insulating film 16 a.

In the above-mentioned first and second embodiments, the secondelectrically insulating film 17 is designed to have its end deviatedfrom an end of the first electrically insulating film 16 in the terminalarea extending outside a pixel located outermost in the display area,specifically, the second electrically insulating film 17 extendsoutwardly from an end of the first electrically insulating film 16, andin addition, the second electrically insulating film 17 is designed tohave a thickness in the predetermined range. Thereby, it would bepossible to prevent a variance in a thickness of the resist used forpatterning the reflection electrode 18, and, further preventunintentional parasitic capacity and short-circuiting between adjacentpixels both caused by the non-removed portion 18 a of the reflectionelectrode 18 (see FIG. 3G).

The above-mentioned first and second embodiments may be applied to acontact area where the reflection electrode 18 is electrically connectedto the source electrode 15 of the thin film transistor 3. Specifically,the second electrically insulating film 17 is designed to extendinwardly from the first electrically insulating film 16 by a certainlength at the contact area. This ensures that a step formed by the firstand second electrically insulating films 16 a and 17 in the vicinity ofthe contact are can be smoothed. Hence, it would be possible to have thesame advantages as those presented by the first and second embodiments.

While the present invention has been described in connection withcertain preferred embodiments, it is to be understood that the subjectmatter encompassed by way of the present invention is not to be limitedto those specific embodiments. On the contrary, it is intended for thesubject matter of the invention to include all alternatives,modifications and equivalents as can be included within the spirit andscope of the following claims.

The entire disclosure of Japanese Patent Application No. 2001-024237filed on Jan. 31, 2001 including specification, claims, drawings andsummary is incorporated herein by reference in its entirety.

1. A method of fabricating a liquid crystal display device, comprisingthe steps at least of: (a) randomly patterning an electricallyinsulating film on a first substrate on which a switching device isfabricated, said electrically insulating film having a wavy surface; and(b) forming a reflection electrode on said wavy surface of saidelectrically insulating film such that said reflection electrode iselectrically connected to an electrode of said switching device, saidreflection electrode reflecting a light passing through both a secondsubstrate facing and spaced away from said first substrate and a liquidcrystal layer sandwiched between said first and second substrates, saidstep (b) including: (b1) forming said electrically insulating film oversaid first substrate; and (b2) patterning said electrically insulatingfilm into a removal region in which said electrically insulating film iscompletely removed, a thin region in which said electrically insulatingfilm remains as a thin film, and a thick region in which saidelectrically insulating film remains as a thick film such that said thinregion extends outwardly from said thick region by a certain length atan end of a display region in which images are to be displayed, therebya step formed by said electrically insulating film in the vicinity ofsaid end of said display region is smoothed.
 2. The method as set forthin claim 1, wherein said electrically insulating film is patterned insaid step (b2) in single exposure to a light through the use of ahalf-tone mask having a light-permeable portion for defining saidremoval region, a half-light-permeable portion for defining said thinregion, and a light-impermeable portion for defining said thick region.3. The method as set forth in claim 2, wherein said half-light-permeableportion is located adjacent to said light-permeable portion.
 4. Themethod as set forth in claim 1, wherein said electrically insulatingfilm is patterned in said step (b2) in single exposure to a lightthrough the use of a photo mask having a light-permeable portion fordefining said removal region, and a half-light-permeable portion fordefining said thin region.
 5. The method as set forth in claim 1,wherein said electrically insulating film is patterned in said step (b2)in single exposure to a light through the use of a photo mask havingsuch a fine pattern that a light to be directed to said thin region isattenuated.
 6. The method as set forth in claim 1, wherein said certainlength is in the range of about 10 μm to about 12 μm both inclusive. 7.The method as set forth in claim 1, wherein said thin region has athickness in the range of about 0.3 μm to about 1.5 μm both inclusive.8. The method as set forth in claim 1, wherein said thick region has athickness in the range of about 1 μm to about 3 μm both inclusive. 9.The method as set forth in claim 1, wherein said electrically insulatingfilm is composed of thermo-flexible organic or inorganic material. 10.The method as set forth in claim 1, wherein said step (c) includes thesteps of: (c1) depositing a material of which said reflection electrodeis composed, entirely over said second electrically insulating film;(c2) coating a resist over said material; (c3) removing said resist inan area in which said material is to be removed; and (c4) etching saidmaterial with said resist being used as a mask.
 11. A method offabricating a liquid crystal display device, comprising the steps atleast of: (a) randomly patterning an electrically insulating film on afirst substrate on which a switching device is fabricated, saidelectrically insulating film having a wavy surface; and (b) forming areflection electrode on said wavy surface of said electricallyinsulating film such that said reflection electrode is electricallyconnected to an electrode of said switching device, said reflectionelectrode reflecting a light passing through both a second substratefacing and spaced away from said first substrate and a liquid crystallayer sandwiched between said first and second substrates, said step (b)including: (b1) forming said electrically insulating film over saidfirst substrate; and (b2) patterning said electrically insulating filminto a removal region in which said electrically insulating film iscompletely removed, a thin region in which said electrically insulatingfilm remains as a thin film, and a thick region in which saidelectrically insulating film remains as a thick film such that said thinregion extends inwardly from said thick region by a certain length at acontact region where said reflection electrode is electrically connectedto said electrode of said switching device, thereby a step formed bysaid electrically insulating film in the vicinity of said contact regionis smoothed.
 12. The method as set forth in claim 11, wherein saidelectrically insulating film is patterned in said step (b2) in singleexposure to a light through the use of a half-tone mask having alight-permeable portion for defining said removal region, ahalf-light-permeable portion for defining said thin region, and alight-impermeable portion for defining said thick region.
 13. The methodas set forth in claim 12, wherein said half-light-permeable portion islocated adjacent to said light-permeable portion.
 14. The method as setforth in claim 11, wherein said electrically insulating film ispatterned in said step (b2) in single exposure to a light through theuse of a photo mask having a light-permeable portion for defining saidremoval region, and a half-light-permeable portion for defining saidthin region.
 15. The method as set forth in claim 11, wherein saidelectrically insulating film is patterned in said step (b2) in singleexposure to a light through the use of a photo mask having such a finepattern that a light to be directed to said thin region is attenuated.16. The method as set forth in claim 11, wherein said certain length isin the range of about 10 μm to about 12 μm both inclusive.
 17. Themethod as set forth in claim 11, wherein said thin region has athickness in the range of about 0.3 μm to about 1.5 μm both inclusive.18. The method as set forth in claim 11, wherein said thick region has athickness in the range of about 1 μm to about 3 μm both inclusive. 19.The method as set forth in claim 11, wherein said electricallyinsulating film is composed of thermo-flexible organic or inorganicmaterial.
 20. The method as set forth in claim 11, wherein said step (c)includes the steps of: (c1) depositing a material of which saidreflection electrode is composed, entirely over said second electricallyinsulating film; (c2) coating a resist over said material; (c3) removingsaid resist in an area in which said material is to be removed; and (c4)etching said material with said resist being used as a mask.